1. Field of the Invention
The invention is in the field of controls for activating electrical loads in motor vehicles.
2. Description of the Prior Art
In the past, several systems have been proposed for activating the headlights of a motor vehicle in response to engine and/or vehicle speed. Some of such devices have incorporated optical and mechanical means such as lights and photosensitive devices mounted on a speedometer. Devices using such mechanical and/or optical modifications to a motor vehicle speedometer in order to control vehicle lighting are shown in U.S. Pat. No. 3,310,774 to Marian, U.S. Pat. No. 3,732,539 to Easterly, and U.S. Pat. No. 3,171,058 to Ono.
Systems have also been proposed which utilize ignition pulses, indicative of engine speed, to bias on electronic switching devices, and therefore to activate relays which in turn energize an electrical load. Such systems are shown in U.S. Pat. No. 3,497,708 to Daugherty and U.S. Ser. No. 308,474, filed Nov. 21, 1972, and assigned to the assignee of the present application. These systems do not show the use of a reference voltage, for comparison purposes with the voltage produced by ignition pulses, nor do these prior art systems show the combination of a control system responsive to engine speed with circuitry responsive to changes in ambient light or the activation of the motor vehicle windshield wipers.